1. Field of the Invention
The present invention relates to an orientation division type liquid crystal display device and a fabrication method thereof and, particularly, the present invention relates to an orientation division type liquid crystal display device of an active matrix drive type, which has a COT (Color filter on TFT) structure in which color filters are arranged on a pixel electrode side substrate having TFT (Thin Film Transistor) switching elements, which is capable of widening a viewing angle of pixel display. Furthermore, the present invention relates to an image display method for use in the orientation division type liquid crystal display device to widen a viewing angle of the pixel display.
2. Description of the Prior Art
The liquid crystal display device has been utilized in various fields as a display device for a television receiver, personal computer and projector, etc., due to the merits of lightweight and low power consumption characteristics thereof. Particularly, the color liquid crystal display device has become popular and the image display mode thereof has been expanded to a monochromatic display, multi-color display and full color display according to objects and use.
As a drive system of the color liquid crystal display, there is an active matrix drive type color liquid crystal display having a switching element such as silicon TFT provided for each of a number of display pixels for controlling a write operation of signal voltage.
With the recent improvement in fineness and coloring of a liquid crystal display device, the increase of the viewing angle of a pixel color layer region of color filters has been required in view of the image contrast and clearness of image display. In order to accommodate to such request, there have been various proposals for increasing the viewing angle by controlling orientation of liquid crystal molecules.
For example, Japanese Patent Publication of Non-Examined Application No. H7-311383 discloses a liquid crystal orientation control in which a slope portion of a transparent electrode film of ITO (Indium Tin Oxide) is provided to control the orientation of liquid crystal molecules along the slope surface.
Furthermore, an opening portion or a protruding portion is provided in a transparent electrode on the side of an opposing substrate and, in combination with the orientation control slope of the pixel electrode, the orientation of liquid crystal molecules is controlled.
In Japanese Patent Publication of Non-Examined Application No. H8-152639, a surface of an opposing substrate on which color filters are provided correspondingly to pixel electrodes on a pixel electrode substrate is made corrugated to divide the orientation direction of liquid crystal molecules to a plurality of orientation directions along the protruding portions thereof.
Under the circumstances, it is usual in the conventional color liquid crystal display device including the above mentioned prior arts to provide pixel color layers as color filters of each of pixels on the side of an opposing substrate.
On the other hand, there is an active matrix drive type liquid crystal display device having a COT structure which includes the pixel color layers as color filters arranged on the side of a pixel electrode substrate.
By employing the COT structure in each pixel region (G, R, B) of a pixel electrode array, it is possible to concentrate the complicated fabrication process for a drain electrode, a drain wiring, a gate electrode and a gate wiring, etc., in four peripheral sides of the pixel electrode on the side of one of the substrates to thereby facilitate the fabrication and reduce the process load.
Furthermore, it is usual in one pixel region to provide a black matrix (BM) layer between adjacent pixel color layers and between corresponding pixel electrode arrays. In such COT structure, four peripheral sides of each pixel electrode are separated from those of adjacent pixel electrodes by the BM layer while utilizing the above-mentioned merits in fabrication process. It is easy to form the BM layer thicker than a usual BM layer.
The conventional liquid crystal display devices described hereinbefore do not employ the COT structure. That is, color filters are arranged on the side of the opposing substrate and the slope portions, etc., are formed on the side of the opposing substrate to divide the orientation of liquid crystal molecules to thereby widen the viewing angle of the pixel display.
There is no detail description of formation of slopes in Japanese Patent Publication of Non-Examined Application No. H8-152639. Assuming that such slope is formed, for example, on or through a step portion provided on the side of an opposing substrate, the initial orientation of liquid crystal molecules on the side of the opposing substrate become opposite to the initial orientation of liquid crystal molecules on the side of the pixel electrode substrate, so that it is impossible to evenly divide orientation of liquid crystal molecules to a plurality of directions.
In the proposal disclosed in the above-mentioned Japanese Patent Publication of Non-Examined Application No. H7-311383, a transparent electrode of an opposing substrate is formed on an insulating layer to step up the transparent electrode to thereby form a slope as an orientation control dislocation layer.
However, since the orientation control dislocation layer is usually formed by etching SiNx or SiO2, etc., it is not easy to form a clearly defined step portion.
Furthermore, it is very difficult to control the initial orientation of liquid crystal molecules to a desired angle by such gentle slope formed on such small step portion. Therefore, it is very difficult to shorten the response time by more clearly dividing the initial orientation direction.
An object of the present invention is to provide, in a liquid crystal display device including a substrate having a COT structure in which pixel color layers as color filters and pixel electrodes are provided on the substrate and various electrodes or electrode wiring are concentrically provided in peripheries of the pixel color layers, an orientation division type liquid crystal display device, which is superior in response time for initial orientation, capable of clearly and evenly dividing the orientation direction to a plurality of directions to thereby widen a viewing angle of pixel display.
Another object of the present invention is to provide a method of fabricating such orientation division type liquid crystal display devices.
A further object of the present invention is to provide an image display method for widening the viewing angle of a pixel display.
As a result of studies made by the inventors of the present invention in order to solve the problems of the prior art, it has been found that it is possible to relatively easily form a step portion in a peripheral portion of a pixel electrode during a forming process of a black matrix (3M) layer provided between adjacent pixel color layers provided correspondingly to the pixel electrode.
That is, according to the present invention, an orientation division type liquid crystal display device is featured in that a substrate opposing to an opposing substrate on which a common electrode is formed has a COT structure in which pixel color layers as color filters and
pixel electrodes are provided on the substrate and a slope having a clear angle with respect to a surface of the opposing substrate is provided in a periphery of each of four sides of the pixel electrode.
The slope may be formed on at least one of a gate electrode, a gate wiring, a drain electrode, a drain wiring and a source electrode, which are provided in the peripheral portion of the pixel electrode.
Alternatively, the slope may be formed on a step portion formed by the BM layer from on one of the electrodes and one of the wiring, which has a vertical height clearly defined with respect to a plane of the pixel electrode.
According to the present invention, an orientation division type liquid crystal display device in which a similar slope is formed on a step portion formed by overlapping edge portions of adjacent pixel color layers is provided.
Liquid crystal molecules filling a space between the substrate and the opposing substrate are aligned vertically with respect to surfaces of the slopes provided in the peripheries of the four sides of the pixel electrode, so that orientation of liquid crystal molecules on the pixel electrode is divided to a plurality of directions by the slope.
According to the present invention, a method for fabricating the orientation division type liquid crystal display device is provided, which comprises the steps of arranging a pixel electrode substrate having pixel color layers as color filters and pixel electrodes thereon and slope surfaces in peripheries of four sides of each pixel electrode in an opposing relation to an opposing substrate, filling a space between the pixel electrode substrate and the opposing substrate with liquid crystal molecules so that orientation of liquid crystal molecules can be controlled by the slope surfaces.
That is, in this fabrication method, the pixel color layers corresponding to the pixel electrode are formed on an insulating layer such as an insulating film or a passivation film on the pixel electrode substrate.
Then, the step portions are formed by the BM layer having thickness larger than a thickness of the pixel color layers and partitioning the pixel color layers.
Below the BM layer forming the step portion, a passivation film is formed as an underlying layer and, below the passivation film, at least one of the gate electrode, the gate wiring, the drain electrode, the drain wiring and the source electrode is formed as an underlying layer.
Then, an overcoat layer is formed on the whole surface of the pixel electrode substrate and, after the transparent pixel electrodes are formed, an alignment layer is formed on the whole surface of the pixel electrode substrate. Thus, the slope surfaces, which surround the four sides of each pixel electrode, are formed on the step portion formed by the BM layer.
According to this fabrication method, it is possible to concentrically form the slope surfaces for dividing the orientation of liquid crystal on the side of the pixel electrode substrate during the step of forming the COT structure, while reducing the process load by the use of the COT structure.
According to the present invention, a method for fabricating the orientation dividing type liquid crystal display device is featured by in that the BM layer is formed on only a portion of the periphery of the pixel electrode and the step portion is formed by partially overlapping edge portions of adjacent ones of the color filter films during the formation of the pixel color layers corresponding to the pixel electrode and the slope surfaces are formed on the step portion.
Furthermore, according to the present invention, an image display method is provided, which uses the orientation division type liquid crystal display device and comprises the step of performing an initial orientation control through the slope surfaces to widen the viewing field of pixel display to thereby clarify the pixel display.
That is, by forming the clearly defined slope surfaces in the peripheries of the four sides of each pixel electrode, liquid crystal molecules on the pixel electrode between the opposing substrate and the pixel electrode substrate become in company with liquid crystal molecules preliminarily oriented vertically to the slope surfaces with an aid of an electric field, which is bulged in an area surrounding the pixel electrode when the orientation direction is changed by applying a voltage across the liquid crystal layer, so that it is possible to immediately determine the alignment direction.
Therefore, it is possible to substantially reduce the response time of initial orientation of liquid crystal molecules within the cell gap and it is possible to evenly divide orientation of liquid crystal molecules on the pixel electrode to a plurality of directions to thereby widen the viewing angle of the pixel display in the pixel region.